<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>$符号</title>
     <script src="../../js/jquery-1.4.2.js"></script>
    <style>
        #d1{
            width:100px;
            height: 100px;
            border:1px solid #000;
        }
    </style>
</head>
<body>
    <div id="d1">

    </div>
</body>
<script>
    //$("div").css("background","red")
    jQuery("#d1").css("background","blue")
</script>
</html>